WO2012035035A1

WO2012035035A1 - Device for treating soot particle-containing exhaust gases

Info

Publication number: WO2012035035A1
Application number: PCT/EP2011/065886
Authority: WO
Inventors: Rolf BRÜCK; Jan Hodgson; Christian Vorsmann
Original assignee: Emitec Gesellschaft Für Emissionstechnologie Mbh
Priority date: 2010-09-15
Filing date: 2011-09-13
Publication date: 2012-03-22
Also published as: EP2616646B1; KR20130051011A; RU2013116733A; CN103119257A; KR101503619B1; CN103119257B; US8906315B2; RU2538217C2; JP5883007B2; DE102010045508A1; EP2616646A1; US20130216440A1; JP2013540937A

Abstract

The invention relates to a device (1) for treating soot-particle (2) containing exhaust gases, comprising at least one ionization element (3) for ionizing soot particles (2), at least one filter element (4), an electric potential being applicable to at least one section of the filter element (4), and at least one flow guiding device (8). Said flow guiding device may influence a flow of the exhaust gases in such a way that the soot particles (2) can be prevented from being deposited on at least one electric insulation (9.1, 9.2) of the ionization element (3) or of the filter element (4) or can be removed therefrom. The invention effectively prevents soot particles (2) from being deposited on an electric insulation (9.1, 9.2) of exhaust gas cleaning components, thereby preventing short-circuits from being produced. In this way, the exhaust gas systems can be safely operated.

Description

The present invention relates to an apparatus for the treatment of soot particles containing exhaust gas, in particular with a so-called electrostatic filter or electrostatic precipitator. The invention finds particular application in the treatment of exhaust gases of mobile internal combustion engines in the automotive sector, in particular in the treatment of exhaust gases resulting from diesel fuel.

In motor vehicles with mobile internal combustion engines and especially in motor vehicles with diesel engines are regularly amounts of soot particles contained in the exhaust gas of the internal combustion engine, which must not be discharged into the environment. This is predetermined by corresponding exhaust regulations that specify limit values for the number and mass of soot particles per exhaust gas weight or exhaust gas volume and in some cases also for an entire motor vehicle. Soot particles are in particular unburned carbons and hydrocarbons in the exhaust gas.

A large number of different concepts for removing soot particles from exhaust gases of mobile internal combustion engines have already been discussed. In addition to mutually closed wall-flow filters, open bypass filters, gravity separators, etc., systems have also been proposed in which the particles are electrically charged in the exhaust gas and then deposited by means of electrostatic attraction forces. These systems are known in particular under the name "electrostatic filter" or "electrostatic precipitator".

In "electrostatic precipitators", the provision of an electric field and / or a plasma causes an agglomeration of small soot particles into larger soot particles and / or an electric charge in soot particles Soot particles are usually much easier to separate in a filter system. Soot particle agglomerates are transported more carrier in an exhaust gas flow due to their greater inertia and thus store easier at deflection of an exhaust gas flow. Electronically charged soot particles are attracted to surfaces due to their charge, to which they attach and release their charge. This also facilitates the removal of soot particles from the exhaust stream in the operation of motor vehicles.

Thus, for such electrostatic filters, a plurality of spray electrodes and collector electrodes are regularly proposed, which are positioned in the exhaust pipe. In this case, for example, a central spray electrode, which runs approximately centrally through the exhaust pipe, and a surrounding jacket surface of the exhaust pipe as a collector electrode used to form a capacitor. With this arrangement of the spray electrode and the collector electrode, an electric field is formed transversely to the flow direction of the exhaust gas, wherein the spray electrode, for example, can be operated with a high voltage which is in the range of about 15 kV. As a result, in particular corona discharges can be formed by which the particles flowing with the exhaust gas through the electric field are charged in a unipolar manner. Due to this charge, the particles migrate to the collector electrode due to the electrostatic coulombic forces. In addition to systems in which the exhaust pipe is designed as a collector electrode, systems are also known in which the collector electrode, for example, is designed as a wire grid. In this case, the attachment of particles takes place on the wire grid for the purpose of possibly combining the particles with other particles, so as to realize an agglomeration. The exhaust gas flowing through the grid then rips the larger particles with them and leads them to classical filter systems.

In the regeneration of filter systems, in addition to the intermittent regeneration by brief heating, that is, burning of the soot (catalytically motivated, oxidative conversion), also known To convert carbon black by means of nitrogen dioxide (NO). The advantage of continuous regeneration with nitrogen dioxide is that the conversion of soot can already take place at significantly lower temperatures (in particular less than 250 ° C.). For this reason, continuous regeneration is preferred in many applications. However, this leads to the problem that it must be ensured that the nitrogen dioxide in the exhaust gas comes into contact with the deposited soot particles to a sufficient extent. Also in this context, there are technical difficulties in the realization of a permanent operation of such exhaust systems in motor vehicles, the different loads of the internal combustion engines lead to different exhaust gas streams, exhaust gas compositions and / or temperatures.

In addition, it should be noted that in the provision of such components for such a soot deposition system as simple as possible components should be used, especially those that can be produced inexpensively in the context of mass production. In addition, especially in the design of the electrodes to take into account that they may need to be positioned aligned in the exhaust pipe, in particular so that an undesirably high dynamic pressure or an undesirable turbulence of the exhaust gas in the region of the electrode does not occur.

Even if the systems described above have proven to be suitable for the treatment of soot particles, at least in tests, the implementation of this concept for series production in motor vehicles poses a great challenge. In particular, the electrical insulation of the electrode and the counter electrode to the exhaust pipe soot particles, whereby a soot particle layer can lead to a short circuit. On this basis, it is an object of the present invention, at least partially solve the problems described with reference to the prior art. In particular, an apparatus for the treatment of soot particles containing exhaust gas is to be specified, which prevents the formation of short circuits on electrical insulation of time.

These objects are achieved with a device according to the features of patent claim 1. Further advantageous embodiments of the device are given in the respectively dependent formulated patent claims. It should be noted that the features listed individually in the claims can be combined with each other in any technologically meaningful manner and show further embodiments of the invention. The description, in particular in conjunction with the figures, explains the invention and provides additional embodiments.

The device according to the invention for treating exhaust gas containing soot particles comprises at least

at least one ionization element for the ionization of soot particles, at least one filter element, wherein an electrical potential can be applied to at least one section of the filter element,

at least one flow guiding device, which can influence a flow of the exhaust gas in such a way that deposition of the soot particles on at least the ionizing element or an electrical insulation of the filter element can be prevented or eliminated.

The device proposed here may in particular be part of an exhaust system of a motor vehicle which has a diesel engine and is arranged in particular in an exhaust pipe of the exhaust system.

Accordingly, the exhaust gas containing the soot particles flows through an ionization element comprising at least one electrode to which a high electric voltage between 3 kV [kilovolt] and 50 kV, preferably between 5 kV and 25 kV can be applied. The tension is So set or regulated or controlled so that it comes to a corona discharge between the electrode and a counter electrode. The ionization element can be formed as a simple spray electrode or rod electrode, but it is preferred that the ionization element comprises a honeycomb body with a plurality of channels through which at least one electrode is arranged at the inlet region or outlet region, which is oriented in or against the flow direction is. The honeycomb body may in particular, at least partially, preferably be formed entirely of an electrically conductive material, so that an electrical potential can be applied to the honeycomb body and thus simultaneously to the electrodes.

Likewise preferably, the at least one ionization element may have an outer tube and an inner tube arranged concentrically therewith, which form a gap traversed by the exhaust gas, wherein at least one annular electrode having a plurality of electrode tips protruding radially into the intermediate space is arranged on the inner tube. The at least one filter element is preferably designed as a surface separator having a plurality of channels, which are permeable to the exhaust gas and extending between an inlet region and an outlet region. By virtue of the electrical potential that can be applied to at least one section of the filter element, the filter element can be used as a counter electrode to the electrode of the ionization elements and the soot particles deposited in the filter element can be neutralized.

The at least one filter element is particularly preferably a so-called open bypass filter in which there are no completely closed flow channels. Rather, the filter element is formed with a metallic fleece and metallic corrugated layers in which openings, guide structures, etc. are provided. The guide structures form flow bottlenecks in the flow passages, so that the residence time or impact probability for soot particles in the interior of the filter element is increased. In this context, reference is made to the applicant's known patent publications which can be used to further characterize the filter element and / or its regeneration; In particular, reference is made in full to the description of the following documents: WO-A-01/80978; WO-A-02/00326; WO-A-2005/099867; WO-A-2005/066469; WO-A-2006/136431; WO-A-2007 / 140,932th The regeneration of such a filter element is preferably carried out continuously based on the CRT method. For this purpose, the device z. B. upstream of an oxidation catalyst in which (also) nitric oxide is oxidized to nitrogen dioxide, which then reacts with the soot in the filter element. In addition, it is also possible that such an oxidatively acting coating is realized in the filter element itself, either in a zone thereof or in all areas of the filter element.

The at least one flow-guiding device is arranged in the flow direction of the exhaust gas in front of the at least one ionization element or in front of the at least one filter element. The flow-guiding device comprises elements which deflect at least one (spatially limited) part of the exhaust gas, in particular in that a part of the exhaust gas flows around the flow-conducting device at least in sections, so that the deflection is influenced only by the shape of the flow-guiding device. The diversion of the partial exhaust gas flow takes place in such a way that soot particles either do not reach the ionization element (and in particular an electrical insulation of the ionization element) or the electrical insulation of the filter element, or hit it in such a way that the exhaust gas flow acts there in that an accumulation of the soot particles is not possible. The avoidance of a soot layer on the electrical insulation and / or the ionization element also causes the formation of a short circuit between the ionizing element and / or the filter element with the exhaust pipe prevented.

Preferably, the flow guiding device comprises at least one element of the following group:

at least one flow straightener,

- At least one baffle.

Under flow rectifier is a device to understand that at least partially reduces the turbulence in a flow or the exhaust flow laminarized and thus produces a more uniform velocity distribution of the exhaust gas over the cross section of the exhaust pipe. This can be done, for example, by a honeycomb body with a plurality of channels through which the exhaust gas can flow.

It is particularly advantageous if the flow-guiding device is adjustable. Thus, by adjusting the flow-guiding device, the flow direction of a part of the exhaust gas leaving the flow-guiding device can be changed. In particular, after predeterminable intervals or due to vehicle parameters, the flow-guiding device is adjusted such that alternating regions of the ionization element or the filter element are flowed through by the exhaust gas, whereby deposition of soot particles on the ionization element or the electrical insulation is prevented or entrained soot particles and thus entrained be eliminated.

In order to prevent deposition of the soot particles on the ionizing element or the electrical insulation of the filter element, the Strömungsleiteinrichtung advantageously forms a flow-through diameter, which is smaller, preferably at least 10% smaller, more preferably at least 25% smaller than a permeable diameter of in Flow direction downstream ionizing element or filter element. In this way, the exhaust gas does not reach the ionizing element or the electrical element surrounding the filter element. see insulation. A deposition of the soot particles thus does not take place. In particular, in the case of a deflection of the soot particles by the electric field of the ionization element, the charged soot particles can not reach the ionization element and / or the electrical insulation of the filter element.

In a development of the invention, it is proposed that the at least one flow-guiding device contains a catalytic reactor. In this way, the exhaust gas flowing past the flow-guiding device can be catalytically converted.

Preferably, the at least one flow guide is attached directly to an exhaust pipe, so that can be dispensed with further fastening elements for the flow guide.

A further development of the invention provides that the at least one flow guide forms a flow shadow in the region of the electrical insulation, which also prevents deposition of the soot particles at least on the ionization element or the electrical insulation of the filter element. The flow guide is thus arranged in the exhaust gas flow, that the exhaust gas does not flow through the ionization element or the electrical insulation of the filter element. In order to prevent deposition of soot particles at least on the ionization element or the electrical insulation and to remove already deposited soot particles, it is also proposed that the at least one flow guide device form a concentrated flow in the area of the electrical insulation with an increased exhaust gas velocity. The exhaust gas velocity is thus increased in relation to the average exhaust gas velocity or the exhaust gas velocity over the cross section of the exhaust gas line without the flow guiding device. This pulse increase of the exhaust gas ensures that already deposited particles at least from the ionizing element or the electrical insulation can be eliminated and located in the exhaust particles can not accumulate.

According to a further preferred embodiment, a device is proposed in which the flow guiding device is arranged upstream of the ionization element, and the flow guiding device has a flow-through region which is dimensioned so that ionized soot particles in the exhaust gas at least do not flow from an electric field generated by the ionizing element reach a surface of the ionization element or the electrical insulation of the filter element. This embodiment is particularly preferably combined with an ionization element in which the outer tube and the inner tube arranged concentrically therewith form a gap through which the exhaust gas can pass, wherein at least one annular electrode with a plurality of electrode tips protruding radially into the intermediate space is arranged on the inner tube on the outer tube. This therefore means, in particular, that a flow obstacle is arranged radially starting from at least the outer tube or the inner tube, whose radial extent is selected as a function of a length of the electric field of the ionization element in the flow direction, the strength of the electric field and the exhaust gas velocity, that ionized soot particles at least do not reach the surface of the ionization element or the electrical insulation of the filter element during operation. The main flow of the exhaust gas is therefore limited to a limited part of the gap, with the walls of the ionizing element forms only a small flow of exhaust gas.

The invention and the technical environment will be explained by way of example with reference to the figures. It should be noted that the figures show particularly preferred embodiments of the invention, but this invention is not limited thereto. They show schematically:

Fig. 1: an embodiment of the device according to the invention, and Fig. 2: a further embodiment of the device according to the invention, Fig. 3: yet another embodiment of the invention

Contraption.

1 shows schematically a cross section through an apparatus 1 according to the invention in an exhaust pipe 16. In the flow direction 15 of the exhaust gas containing soot particles 2, an ionization element 3 and a filter device 4 are arranged behind a flow guiding device 8. The flow guiding device 8 comprises a deflecting plate 11, which is fastened to the exhaust gas line 16 via fastening elements (not shown). The ionization element 3 has an electrically conductive honeycomb body 17, which is connected to the exhaust gas line 16 via a first electrical insulation 9.1. At the back of the honeycomb body 17 in the flow direction 15, a plurality of electrodes 14 are arranged, which can be acted upon by a first electrical connection 13.1 with an electrical voltage. The filter element 4 has a plurality of channels 5 through which the exhaust gas can flow and which extend between an inlet region 6 and an outlet region 7. The filter element 4 is insulated from the exhaust pipe 16 with a second electrical insulation 9.2. The filter element 4 can be impacted by a second electrical connection 13.2 with an electrical voltage.

During operation, the exhaust gas containing soot particles 2 flows toward the ionization element 3 and is at least partially deflected by the deflecting plate 11. By the baffle 11, a portion of the exhaust gas is accelerated and hits at an increased speed on the first electrical insulation 9.1, whereby the soot particles 2 can not settle on the first electrical insulation 9.1 or already released on the first electrical insulation 9.1 settled particles become. The exhaust gas also flows through the honeycomb body 17 of the ionization element 3, wherein the flow is at least partially laminarized. In the region between the electrodes 14 and the filter element 4, at least part of the soot particles 2 are ionized in a corona discharge between the electrodes 14 and the filter element 4. The charged soot particles 2 are accelerated toward the filter element 4 and deposited therein due to their charge at a higher deposition rate.

2 schematically shows a cross section through a further exemplary embodiment of the device 1 according to the invention. This embodiment of the device 1 according to the invention has a similar construction to the exemplary embodiment according to FIG. 1, so that only the differences are discussed here. In this embodiment, the flow guide 8 is designed as a flow rectifier 10. The flow rectifier 10 has a flow-through diameter 12 which is smaller than a flow-through diameter of the downstream ionization element 3. In the flow rectifier 10, the exhaust gas flow is at least partially laminarized and reduced to the diameter 12 of the flow rectifier 10 through which it can flow. With sufficient difference in the diameters 12 of the flow rectifier and the ionizing element 3 is thus achieved that the soot particles 2 in the exhaust gas not see the first electrical see 9.1 of the ionization element 3. A deposit on the electrical insulation 9.1 is thus avoided.

3 shows a schematic representation of a sectional view of a further embodiment of the device 1 according to the invention, wherein in the following only the differences from the embodiment according to FIG. 2 will be discussed. The flow guide device 8 has a honeycomb body 17, which holds a counterelectrode 22 of the ionization element 3. The honeycomb body 17 has in an outer and an inner region closed channels 18, which with a radial extension 20 a Prevent flow through the honeycomb body 17 in these areas. Thus, a flow-through region 19 of the honeycomb body 17 is formed. The ionization element 3 has an annular electrode 14 assigned to the exhaust gas line 16 with a multiplicity of electrode tips. Centrally in the exhaust pipe 16, a tubular counter electrode 22 is arranged, which is held by the honeycomb body and possibly isolated from this. Thus, over a length 21, an electric field may be formed between the annular electrode 14 and the tubular counter electrode 22.

The radial extent 20 of the closed channels 18 is selected so that ionized soot particles 2 can not be distracted so far from the electric field present between the annular electrode 14 and the counterelectrode 22 that they can reach a surface of the ionization element 3. The size of the radial extent 20 thus depends essentially on the length 21, the electric field strength and the exhaust gas velocity.

With the present invention, it is effectively prevented that soot particles deposit on an electrical insulation of exhaust gas purification components, thereby preventing the formation of a short circuit. Safe operation of the exhaust system is thus ensured.

LIST OF REFERENCE NUMBERS

1 device

2 soot particles

3 ionization element

4 filter element

5 channel

6 entrance area

7 exit area

8 flow guide

9.1 first electrical insulation

9.2 second electrical insulation

10 flow straightener

11 baffle

12 diameters

13.1 first electrical connection

13.2 second electrical connection

14 electrode

15 flow direction

16 exhaust pipe

17 honeycomb body

18 sealed channels

19 permeable area

20 radial extent

21 length

22 counter electrode

Claims

claims

Device (1) for treating exhaust gas containing soot particles (2), comprising at least

at least one ionization element (3) for ionizing soot particles (2),

at least one filter element (4), wherein an electrical potential can be applied to at least one section of the filter element (4),

- At least one flow guide (8) which can influence a flow of the exhaust gas so that a deposition of the soot particles (2) on at least the ionizing element (3) or an electrical insulation (9.2) of the filter element (4) can be prevented or eliminated ,

Device (1) according to claim 1, wherein the flow-guiding device (8) comprises at least one element of the following group:

at least one flow rectifier (10),

- At least one baffle (11).

Device (1) according to one of the preceding claims, wherein the flow-guiding device (8) is adjustable.

Device (1) according to one of the preceding claims, wherein the flow-guiding device (8) forms a diameter (12) permeable to exhaust gas, which is smaller than a flow-through diameter of the ionization element (3) or filter element (4) downstream in the flow direction (15).

Device (1) according to one of the preceding claims, wherein the at least one flow guide (8) contains a catalytic lytic reactor.

6. Device (1) according to one of the preceding claims, wherein the at least one flow guide (8) is attached to an exhaust gas line (16).

7. Device (1) according to one of the preceding claims, wherein the at least one flow guide (8) forms a flow shadow in the field of electrical insulation (9.1, 9.2).

Device (1) according to one of the claims 1 to 6, wherein the at least one flow guiding device (8) forms a concentrated flow in the region of at least one surface of the ionizing element or the electrical insulation (9.2) with an increased exhaust gas velocity.

Device (1) according to one of the preceding claims, wherein the flow guide (8) is arranged upstream of the ionization element (3), and the flow guide (8) has a flow-through region which is dimensioned such that ionized soot particles in the exhaust gas flow from one through the ionization element (3) generated field do not reach a surface of the ionizing element (3) or the electrical insulation (9.2) of the filter element (4).